This experiment studies the bond strength between old (substrate) and many types of new (repair) concrete. The main aim of this study is to evaluate different approaches to ensure monolithic behavior and effective bonding. Also, evaluate the influence of differential stiffness and differential shrinkage at the interface of concrete layers cast at different ages. The investigation related to bonding strength consisted of studying the effect of many variables: surface preparation, type of bonding agent, age difference, and concrete type of new concrete. The slant shear test results show that, increasing the age of old concrete results in a corresponding decrease in the bonding strength and normal compression stress of the samples. The bonding strength decreases by 16.6, 25.4, and 28% for sample with old concrete age of 7days, 28days, and one year respectively, with respect to the sample with old concrete age of 3days. And, the failure mod of the samples of old concrete age group was the same, which is bond failure. Finally, the sample with SIKA has the highest value of bonding strength, while the sample with steel fibers has the lowest value of bonding strength. The bonding strength increases by 15.3, 40.6, and 44.3% for sample with new concrete of Self-Compacting Concrete (SCC), High Strength Concrete (HSC), and SIKA respectively, with respect to the sample with new concrete of steel fibers.